The present invention concerns certain peptide esters and their uses, for example, in the ablation of certain cell-mediated immune responses. For brevity and clarity, many of the terms used herein have been abbreviated and these abbreviations include those shown in Table 1. Research involved in the development of the invention was supported by grants from the United States government.
L-leucine methyl ester (Leu-OMe) has previously been used as a lysosomotropic agent (Thiele et al. (1983) J. Immunol. V 131, pp 2282-2290; Goldman et al. (1973) J. Biol. Chem. V 254, p 8914). The generally accepted lysosomotropic mechanism involved leu-OMe diffusion into cells and into lysosomes, followed by intralysosomal hydrolysis to leucine and methanol. The more highly ionically charged leucine, largely unable to diffuse out of the lysosome, caused osmotic lysosomal swelling and rupture. The fate of leu-OMe subjected to rat liver lysosomes was additionally suggested by Goldman et al. (1973) to involve a transpeptidation reaction and a resultant species--"presumably the dipeptide" which was "further hydrolyzed to free amino acids". A subsequent and related paper by Goldman (FEBS (Fed. Europ. Biol. Sci.) Letters V 33, pp 208-212 (1973)) affirmed that non-methylated dipeptides were thought to be formed by lysosomes.
L-amino acid methyl esters have been specifically shown to cause rat liver lysosomal amino acid increases (Reeves (1979) J. Biol. Chem. V 254, pp 8914-8922). Leucine methyl ester has been shown to cause rat heart lysosomal swelling and loss of integrity (Reeves et al., (1981) Proc. Nat'l. Acad. Sci., V 78, pp 4426-4429).
TABLE 1 ______________________________________ Abbreviations Substance Symbol ______________________________________ L-leucine leu or L L-phenylalanine phe or P L-alanine ala or Al L-glycine gly or G L-serine ser or S L-tyrosine tyr or T L-arginine arg or Ar L-lysine lys or Ly L-valine val or V L-isoleucine ile or I L-proline pro or P L-glutamic acid glu or G L-aspartic acid asp or As L amino acid methyl esters e.g. Leu--OMe L amino acid ethyl esters e.g. Leu--OEt L amino acid benzyl esters e.g. Leu--OBz D-amino acids e.g. D--Leu D-amino acids methyl esters e.g. D--Leu--OMe dipeptides of L-amino acids e.g. Leu--Leu methyl esters of dipeptide e.g. Leu--Leu--OMe L amino acids or LLOMe dipeptide amides e.g. L--Leu--L--Leu--NH.sub.2 dipeptidyl peptidase-I DPPI ______________________________________ cell fraction or type Symbol ______________________________________ mononuclear phagocytes MP polymorphonuclear leucocytes PMN natural killer cells NK peripheral blood lymphocytes PBL peripheral blood mononuclear cells PBM cytotoxic T-lymphocytes CTL glass or nylon wool adherent cells AC glass or nylon wool non-adherent NAC cells Other Materials phosphate buffered saline PBS thin layer chromatography TLC fluorescence activated cell sorter FACS mixed lymphocyte culture MLC Miscellaneous effector:target cell ratio E:T fetal bovine serum FBS University of Texas Health UTHSCD Science Center, Dallas, Texas. Standard error of mean SEM probability of significant p difference (Student's t-test) Graft versus host disease GVHD Maximum velocity Vmax Micromolar micro-M Level at which there is a LD.sub.50 50% loss of cell function Trichloracetic acid TCA Phenylmethylsulfonyl fluoride PMSF Glycylphenylalanine diazomethane Gly--Phe--CHN.sub.2 Mean survival time MST ______________________________________
Natural killer cells are large granular lymphocytes that spontaneously lyse tumor cells and virally-infected cells in the absence of any known sensitization. This cytotoxic activity can be modulated by a host of pharmacologic agents that appear to act directly on NK effector cells. NK activity has been shown to be augmented after exposure to interferons (Gidlund et al., Nature V 223, p 259), interleukin 2, (Dempsey, et al. (1982) J. Immunol. V 129, p 1314) (Domzig, et al. (1983) J. Immunol. V 130, p 1970), and interleukin 1 (Dempsey et al. (1982) J. Immunol. V 129, p 1314), whereas target cell binding is inhibited by cytochalasin B, (Quan, et al. (1982) J. Immunol. V 128, p 1786), dimethyl sulfoxide, 2-mercaptoethanol, and magnesium deficiency (Hiserodt, et al. (1982) J. Immunol. V 129, p 2266). Subsequent steps in the lytic process are inhibited by calcium deficiency (Quan et al. (1982) J. Immunol. V 128, p 1786, Hiserodt, et al. (1982) J. Immunol. V 129, p 2266), lysosomotropic agents (Verhoef, et al. (1983) J. Immunol. V 131, p 125), prostaglandin E.sub.2 (PGE.sub.2 (Roder, et al. (1979) J. Immunol. V 123, p 2785, Kendall, et al. (1980) J. Immunol. V 125, p 2770), cyclic AMP (Roder, et al. (1979) J. Immunol. V 123, p 2785, Katz (1982) J. Immunol. V 129, p 287), lipomodulin (Hattori, et al. (1983) J. Immunol. V 131, p 662), and by antagonists of lipoxygenase (Seaman (1983) J. Immunol V 131 p 2953). Furthermore, it has been demonstrated that PGE.sub.2 and reactive metabolites of oxygen produced by monocytes (MP) or polymorphonuclear leukocytes (PMN) can inhibit NK cell function (Koren, et al. (1982) Mol. Immunol. V 19, p 1341; and Seaman, et al. (1982) J. Clin. Invest. V 69, p 876).
Previous work by the present applicants has examined the effect of L-leucine methyl ester on the structure and function of human peripheral blood mononuclear cells (PBM) (Thiele, et al. (1983) J. Immunol. V 131, p 2282.
Human peripheral blood mononuclear cells (PBM) are capable of mediating a variety of cell-mediated cytotoxic functions. In the absence of any known sensitization, spontaneous lysis of tumor cells and virally-infected cells is mediated by natural killer cells (NK) contained within the large granular lymphocyte fraction of human PBM Timonen et al. (1981) v. J. Exp Med. V 153 pp 569-582. After lymphokine activation, additional cytotoxic lymphocytes capable of lysing a broad spectrum of tumor cell targets can be generated in in vitro cultures (Seeley et al. (1979) J. Immunol. V 123, p 1303; and Grimm et al. (1982) J. Exp. Med. V 155, p 1823). Furthermore, lymphokine activated peripheral blood mononuclear phagocytes (MP) are also capable of lysing certain tumor targets (Kleinerman et al. (1984) J. Immunol. V 133, p 4). Following antigen-specific stimulation, cell-mediated lympholysis can be mediated by cytotoxic T lymphocytes (CTL).
While a variety of functional and phenotypic characteristics can be used to distinguish these various types of cytotoxic effector cells, a number of surface antigens and functional characteristics are shared. Thus, the antigens identified by the monoclonal antibodies OKT8 (Ortaldo et al. (1981) J. Immunol. V 127, p 2401; and Perussia et al. (1983) J. Immunol. V 130, p 2133), and OKT11 (Perussia et al. (1983) J. Immunol. V 130, p 2133; and Zarling et al. (1981) J. Immunol. V 127, p 2575) are found on both CTL and NK while the antigen identified by OKM1 is shared by MP and NK (Zarling et al. (1981) J. Immunol. V 127, p 2575; Ortaldo et al. (1981) J. Immunol. V 127, p 2401; Perussia et al. (1983) J. Immunol. V 130, p 2133; and Breard et al. (1980) J. Immunol. V 124, p 1943. Furthermore, cytolytic activity of both NK and MP is augmented by interferons, (Kleinerman et al. (1984) J. Immunol. V 133, p 4; Gidlund et al. (1978) Nature V 223, p 259; and Trinchieri et al. (1978) J. Exp. Med. V 147, p 1314). Finally, use of metabolic inhibitors has demonstrated some parallels in the lytic mechanism employed by CTL and NK (Quan et al. (1982) J. Immunol. V 128, p 1786; Hiserodt et al. (1982) J. Immunol. V 129, p 1782; Bonavida et al. (1983) Immunol. Rev. V 72, p 119; Podack et al. (1983) Nature V 302, p 442; Dennert et al. (1983) J. Exp. Med. V 157, p 1483; and Burns et al. (1983) Proc. Nat'l. Acad. Sci. V 80, p 7606).